mx28evk: Add documentation on how to boot from SPI NOR

Explain the necessary steps in order to boot from SPI NOR.

Based on a earlier submission from Mårten Wikman.

Signed-off-by: Mårten Wikman <marten.wikman@novia.fi>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
diff --git a/board/freescale/mx28evk/README b/board/freescale/mx28evk/README
index 0389a1d..958ebc6 100644
--- a/board/freescale/mx28evk/README
+++ b/board/freescale/mx28evk/README
@@ -23,11 +23,19 @@
    * VDD 5V: To the left (off)
    * Hold Button: Down (off)
 
+To boot MX28EVK from SPI NOR flash, set the boot mode DIP switches as:
+
+   * Boot Mode Select: 0 0 1 0 (Boot from SSP2)
+   * JTAG PSWITCH RESET: To the right (reset disabled)
+   * Battery Source: Down
+   * Wall 5V: Up
+   * VDD 5V: To the left (off)
+   * Hold Button: Down (off)
 
 Environment Storage
 -------------------
 
-There are two targets for mx28evk:
+There are three targets for mx28evk:
 
 "make mx28evk_config"		- store environment variables into MMC
 
@@ -35,12 +43,20 @@
 
 "make mx28evk_nand_config"	- store environment variables into NAND flash
 
+or
+
+"make mx28evk_spi_config"       - store enviroment variables into SPI NOR flash
+
 Choose the target accordingly.
 
 Note: The mx28evk board does not come with a NAND flash populated from the
 factory. It comes with an empty slot (U23), which allows the insertion of a
 48-pin TSOP flash device.
 
-Follow the instructions from doc/README.mxs to generate a bootable SD card.
+mx28evk does not come with SPI NOR flash populated from the factory either.
+It is possible to solder a SOIC memory on U49 or use a DIP8 on J89.
+To get SPI communication to work R320, R321,R322 and C178 need to be populated.
+Look in the schematics for the proper component values.
 
-Insert the SD card in slot 0, power up the board and U-boot will boot.
+Follow the instructions from doc/README.mxs to generate a bootable SD card or
+to generate a binary to be flashed into SPI NOR.